The present invention relates to thermoprocessable fluorinated polymers having good mechanical and gas and vapour barrier properties.
Specifically the present invention relates to chlorotrifluoroethylene (CTFE) thermoprocessable copolymers with acrylic monomers having improved mechanical and gas and vapour barrier properties in comparison with the CTFE homopolymer (PCTFE).
More specifically the present invention relates to CTFE copolymers with acrylic monomers to be used for packaging applications requiring good impermeability to gases and vapours, more specifically to oxygen, nitrogen and water vapor.
The good CTFE homopolymer impermeability both to gases and to water vapor is known. The high molecular weight polymers show also good mechanical properties but because of the high melt viscosity their processability is difficult and they can give articles having surface defects. On the contrary the polymers having a lower molecular weight are easily processable because of the low melt viscosity but they show poor mechanical properties. In particular the required processability conditions are for the obtainment of films, used also in multilayer systems, for packaging of food and pharmaceutical products.
The need was felt to have available fluorinated polymers having: good gas and vapour barrier properties, specifically water vapor; good mechanical properties; suitable melt viscosity for the film processing.
The Applicant has surprisingly and unexpectedly found CTFE thermoprocessable copolymers with acrylic monomers having good mechanical properties, good gas and vapour -specifically water vapor-barrier properties, and suitable melt viscosities for the film processing.
It is therefore an object of the present invention a thermoprocessable copolymer, having a Melt Flow Index (MFI) between 0.01 and 1000, of the CTFE with an acrylic monomer having the general formula:
CH2xe2x95x90CHxe2x80x94COxe2x80x94Oxe2x80x94R1 xe2x80x83xe2x80x83(I) 
wherein R1 is hydrogenated radical from 1 to 20 C atoms C1-C20, preferably alkyl, linear and/or branched, or cycloalkyl radical, having from 4 to 20 atoms, or R1 is H. The radical R1 can optionally contain: heteroatoms preferably Cl, O, N; one or more functional groups preferably selected from xe2x80x94OH, xe2x80x94COOH, epoxide, ester and ether; and double bonds.
The amount of the comonomer of formula (I) ranges from 0.01 to 5% by moles, preferably from 0.05 to 2% by moles, more preferably from 0.1 to 1% by moles.
R1 is preferably an alkyl radical from 1 to 10 C atoms containing one or more hydroxy functional groups.
As comonomer of formula (I), ethylacrylate, n-butylacrylate, acrylic acid, hydroxyethylacrylate, hydroxypropylacrylate, (hydroxy) ethylhexylacrylate, etc., can be mentioned.
A further object of the present invention is the use of the CTFE copolymers with acrylic monomers having a Melt Flow Index (MFI) between 0.1 and 50, preferably between 0.5 and 20, more preferably between 2 and 10, for the production of films.
The preparation process of the copolymer of the present invention is carried out according to known techniques, by copolymerization of the corresponding monomers, in suspension in organic medium or in aqueous emulsion, in the presence of a suitable radical initiator, at a temperature in the range from xe2x88x9220 to 100xc2x0 C., preferably from xe2x88x925 to 60xc2x0 C., more preferably from 5 to 30xc2x0 C. The reaction pressure is in the range 1-40 bar, preferably 2-20 bar.
Among the various radical initiators, in particular, can be used:
(i) bis-acylperoxides of formula (Rfxe2x80x94COxe2x80x94O)2, wherein Rf is a C1-C10 (per)haloalkyl (see for instance EP 185,242 and U.S. Pat. No. 4,513,129), or a perfluoropolyoxyalkylene group (see for instance EP 186,215 and U.S. Pat. No. 5,021,516); among them, bis-trichloroacetylperoxide and bis-dichlorofluoroacetyl-peroxide, are particularly preferred (see U.S. Pat. No. 5,569,728);
(ii) water soluble inorganic peroxides, such as ammonium or alkaline metals persulphates or perphosphates; sodium and potassium persulphate are particularly preferred;
(iii) organic or inorganic redox systems, such as ammonium persulphate/sodium sulphite, hydrogen peroxide/aminoimi-nomethansulphinic acid, and terbutylhydroperoxide/metabisulphite (see U.S. Pat. No. 5,453,477).
In the suspension copolymerization, the reaction medium is formed by an organic phase, to which water is sometimes added in order to favour the heat dispersion during the reaction. The organic phase can be formed by the monomers themselves, without addition of solvents, or by the monomers dissolved in a suitable organic solvent. As organic solvents, chlorofluorocarbons, such as CCl2F2 (CFC-12), CCl3F (CFC-11), CCl2FCClF2 (CFC-113), CClF2CClF2 (CFC-114), etc., are conventionally used. Since such products have a destroying effect on the ozone present in the stratosphere, alternative products have been recently proposed, such as the compounds containing only carbon, fluorine, hydrogen, and optionally oxygen, described in U.S. Pat. No. 5,182,342. In particular (per)fluoropolyethers with at least one hydrogenated end group, preferably two, such as xe2x80x94CF2H, xe2x80x94CF2CF2H, xe2x80x94CF(CF3)H, can be used.
The amount of water in the reaction medium must be lower than 5% by weight when preparing the copolymers of the present invention in suspension in organic medium wherein R1 contains one or more xe2x80x94OH and/or xe2x80x94COOH groups.
In the aqueous emulsion (co)polymerization, the presence of a suitable surfactant is required. The fluorinated surfactants of formula:
Rfxe2x88x92Xxe2x88x92M+
are the most commonly used, wherein Rfis a C5-C16 (per) fluoroalkyl chain or a (per) fluoropolyoxyalkylene chain, Xxe2x88x92is xe2x80x94COOxe2x88x92 or xe2x80x94SO3xe2x88x92, M+ is selected from: H+, NH4+, an alkaline metal ion. Among them we can mention: ammonium and/or sodium perfluoro-octanoate, (per) fluoropolyoxyalkylenes having one or more one or more carboxylic end groups, etc.
The process object of the present invention can be advantageously carried out in the presence of dispersions, emulsions or microemulsions of perfluoropolyoxyalkylenes, according to U.S. Pat. No. 4,789,717 and U.S. Pat. No. 4,864,006, or also microemulsions of fluoropolyoxyalkylenes having hydrogenated end groups and/or hydrogenated repeating units, according to U.S. Pat. No. 4,498,680.
The addition of the comonomer of formula (I), as such or in solution with the above solvents in polymerization occurs according to known techniques in the art. However a continuous or step addition are particularly preferred in the synthesis of copolymers of the present invention having a composition higher than 0.1% by moles of the comonomer of formula (I).
The molecular weight control of the fluorinated polymers of this invention can be carried out by: a suitable dosage of the radical initiator in polymerization; the use of telogen agents (chain transfer agents); the use of the monomers of formula (I) which can show a telogen activity comparable with the known chain transfer agent. The molecular weight adjustment is preferred in absence of specific telogen agents.
When chain transfer agents are used, these can be hydrocarbons or halogenated hydrocarbons, for instance chloroform, HCFC 123, ethane, methane, etc. The chain transfer agent is introduced into the reactor at the beginning of the reaction, or continuously or step by step during the polymerization. The amount of chain transfer agent can range within rather wide limits, depending on the polymerization conditions (reaction temperature, monomers, molecular weight required of the polymer, etc). Generally, such amount ranges between 0.001 and 5% by weight, preferably between 0.05 and 1% by weight, with respect to the total amount of monomers introduced in the reactor.
A remarkable advantage of the comonomers (c) of the present invention is given by the fact that their high reactivity in the polymerization system of the invention does not require, after reaction, the recovery of the unreacted monomers.
The viscosity measurement of the polymers object of the present invention is made by the Melt Flow Index (MFI) measurement at 265xc2x0 C. and a 5 Kg load according to ASTM D 1238-88.
The second melting temperature (T2f), is determined by differential scanning calorimetry (DSC).
The formula (I) comonomer content is determined by mass balance assuming a quantitative conversion of the comonomer itself. This high reactivity has been confirmed by 1H-NMR analysis of the copolymers exemplified.
The mechanical properties at 23xc2x0 C. have been obtained by the ASTM D1708 method by using compression-molded samples.
The permeability to oxygen has been determined according to the ASTM D1434 method at room temperature (23.5xc2x10.2xc2x0 C.) by using compression-molded sheets having a 0.3 mm nominal thickness.
The permeability to water vapor (Water Vapor Transmition Rate: WVTR) has been determined by the Mocon PERMATRAN W200 equipment according to the ASTM F1249 method by using compression-molded sheets having a 0.3 mm nominal thickness. The method sensitivity is 0.05 g/m2*24 h. The operating conditions are 38xc2x0 C. and RH (relative humidity) is 90%.
Some examples of the present invention are reported hereinafter, whose purpose is merely illustrative and not limitative of the scope of the invention itself.